Exciters designed for operation with synchronous generators have traditionally been required to protect the generator field by limiting operation of the generator in the overexcited region of a generator's capability curve which is restricted by field heating. In the underexcited region of the generator capability curve, operation must be limited because of stator end turn heating and stator lamination over-voltage effects. Operation between rated KVA at rated lagging power factor and rated KVA at unity power factor must be limited because of overheating caused by excessive stator current. While conventional fixed hardware or software algorithms used to implement this functionality such as General Electric's GENERREX-CPS, GENERREX-PPS, SHUNT-SCR, ALTERREX, STATIC BUS FED EXCITATION and SILCO 5 control implementations, can properly protect the generator these prior art implementations do not have any capability of being responsive to coolant conditions as they deteriorate from nominal. A further problem is that prior art limiter implementations do not account for improved coolant conditions and the possible increase in generator rating associated with such improved coolant conditions. Indeed, "ambient following" combustion turbine applications are particularly sensitive to changes in coolant conditions as the output power capability thereof varies significantly with coolant conditions.
It is thus seen to be desirable to coordinate the limit and protection functions of a generator exciter as a function of coolant conditions to provide improved overall generator performance.